This invention relates to an enclosure known within the industry as a valve box. The valve box is used to enclose fluid handling devices, such as a valve and manifold system, for the purpose of containing fluid leaks and, more particularly, specifically designed to provide an improved degree of fluid containment should the system be under pressure.
In certain industries caustic chemicals are used in processing stages that necessitate special handling precautions. The special handling precautions implemented depend upon the particular process operation and the type of product being produced. In instances, the special handling precaution can be limited to the selection of materials, making sure that the material selected to build the fluid handling system does not fail when exposed to the process chemicals. In other instances, it is desired that the material selected to form the wetted portion of the fluid handling system not introduce contaminate materials in the process during use, to thereby avoid contaminating an otherwise ultra-pure process. Further, special handling precautions are taken to provide a containment system around a primary fluid handling device that contains the process fluid, to thereby limit its exposure to the environment and minimize any related health risk or environmental impact, should the primary fluid handling device leak or fail.
In the semiconductor industry, in particular, extremely acidic chemicals are used during the process of making semiconductors. The process of making semiconductors also requires that the processing liquid be of a high purity level, to not contaminate the final product. Therefore, an additional requirement is that the material selected for making the wetted fluid handling device not introduce containment material into the system during processing. Fluorpolymeric tubing is commonly used for transporting chemicals used in the semiconductor processing operation, but is relatively soft and therefore requires use of a secondary containment system to protect against any potential leakage or rupture.
Valves used in the semiconductor industry to transport such chemicals are also contained, to protect against potential leakage, by use of a valve box. Valve boxes are designed to enclose the valve, manifold and associated connecting tubing or hosing, and are intended to withstand both vapor exposure (that can permeate through fluoropolymeric tubing) and short term liquid exposure in the event of a valve, fitting, or tubing leak. Valve boxes known in the art are constructed with flat, opaque polypropylene that is first cut to size, and then air welded together in the form of a box. Polypropylene is selected because it is extremely economical, easy to weld, and durable. Clear PVC is typically used as a window, across the front opening of the box, to allow one to view the fluid handling system contained within. The window is also removable to allow access to the system to make desired valve adjustments and/or inspections.
Such known valve boxes include an O-ring seal that is compressed between the window and the valve box housing, and that operates to prevent leakage of gas or liquid from the valve box. The seal is held in place, between the window and housing, by a plurality of machine screws that extend through opposed flange portions of the window and box. The flange portions are oriented parallel with each other, and with the remaining surfaces of the box and window, and extend along the edge portion of the box and window. The seal is interposed between the two flange portions, and is compressed by the tightened machine screws. This type of seal arrangement is referred to as a xe2x80x9cface sealxe2x80x9d because the seal is simply positioned between the opposed flat face of the window and box flanges. With such a face seal arrangement the seal is compressed in a direction that is parallel to the axis of the screws.
Such known valve boxes also include one or more polypropylene fittings welded to one or more side surfaces of the box for making connections with necessary secondary containment piping and/or for running electrical wires and other noncritical tubing through the box. PVC fittings are threaded into the polypropylene fittings in order to make the transition to the secondary containment system, which must have PVC-to-PVC connections for solvent bonding to be effective. Such a known valve box is typically hung on a wall, or attached to a rack. After the valve has been installed within the box, and all necessary fluid connections made, it is typically tested to ensure that it can serve its intended function. Valve boxes known in the art, constructed in the manner described above, must be able to endure a leak test as part of an overall secondary containment system at a pressure of 1 psig for a period of one hour.
While known valve boxes, constructed in the manner described above, do provide some degree of secondary containment protection to a fluid handling system, they do suffer from some disadvantages. For example, while the use of sheet polypropylene to construct such valve boxes is cost effective from a material perspective, the task of cutting and welding together as many as 15 separate pieces is a time consuming and costly process. Additionally, such construction method produces a box that is heavy for its size, thereby limiting potential mounting and/or placement options.
A major issue and concern associated with such known valve boxes is the seal design and its susceptibility to leaking when the box is pressurized. As pressure builds up within the box, due either to air during a pressure test or to fluid leaking from tubing or the enclosed fluid handling device, it acts to push the window outwardly away from the box opening. This outwardly directed pressure force causes the opposed flanges to be pushed away from one another, i.e., in a direction opposite from the compression force imposed from the machine screws, thereby causing the seal to be unloaded. Such unloading of the seal can result in gas and/or fluid leakage from the valve box.
Another problem with the conventional valve box construction is the design of its box having a flat bottom that opens to the flange. This design does not provide a barrier of any sort to prevent leaking liquid from running out of the box once the window is opened or removed. Another problem with such conventional valve boxes is the use of opaque polypropylene material to build the box, which makes it difficult to observe leaks or drips within, at locations remote from the window. A still other problem associated with such known valve boxes is the need to use polypropylene fittings, as they add unnecessarily to the cost of the box and merely serve as a transition from the polypropylene box to the PVC pipe in the secondary containment system.
Accordingly, it is desired that a valve box be constructed in such a manner that addresses the problems as noted above. It is desired that a valve box be constructed in a manner that: (1) is both time and cost efficient; (2) provides a seal arrangement that is not susceptible to leakage from built up pressure within the housing; (3) protects against the leakage of fluid from the housing upon opening of a valve box lid or window; (4) provides a transparent housing to enable easy visual observation of leaks and drips within the housing; (5) does away with the need to provide polypropylene fittings and (6) provides a reduction in overall weight for installation and handling purposes.
Valve boxes, constructed according to principles of this invention, are configured having a self-energizing sealing arrangement that produces an increased sealing force with increased internal pressure, thereby improving the ability to provide a leak-tight seal in the event of liquid leakage within the box. Valve boxes of this invention generally comprise a housing including an inner chamber that extends axially through the housing from a housing base. The housing chamber includes a diameter that is defined by a housing sidewall surface that extends outwardly from the base, forming a chamber opening. The chamber opening includes a seal surface that is positioned radially inwardly towards the chamber.
The valve box further includes a lid that is positioned over the housing chamber opening. The lid includes a concave center section and a seal surface disposed radially therearound. The lid seal surface is positioned radially towards the chamber, and is placed opposite the chamber opening seal surface. An annular seal is interposed between the housing chamber and lid seal surfaces. The chamber and lid seal surfaces are configured generally perpendicular to the chamber opening such that internal pressure within the chamber causes the concave center portion to impose a radially outwardly directed pressure onto the lid, thereby further compressing the annular seal to ensure a leak-tight seal.